The present invention relates to a deployable mast, particularly for use in space vehicles.
Deployable masts, or lattice columns, are used in a variety of environments, including both space and terrestrial applications. Such columns are subject to destruction, for example by impacting micrometeorites in space applications, or by shrapnel, as when used for military applications in terrestrial environments.
Known structures of this type, disclosed in U.S. Pat. Nos. 3,486,279 and 4,334,391, are composed of three longitudinal members, or longerons, between which are connected a plurality of lateral elements. The lateral elements include both battens and diagonal members, pairs of the diagonal members being cross-connected to generally laterally opposed points along the longerons, thereby defining a bay of the column. In the structure disclosed in U.S. Pat. No. 4,334,391, the diagonal members are connected to the longerons such that adjacent bays substantially overlap. The battens connect the laterally opposed connection points of the diagonal members and serve to tension the diagonal members when the mast is in a deployed state.
The mast components are constructed and interconnected to be movable relative to one another so that when no external forces are imposed, the mast assumes a deployed orientation in which the longerons extend parallel to one another along straight lines or coaxial helices. External forces can be applied to the mast to cause it to assume a stowed configuration in which the mast structure has a significantly shorter length. Movement between the deployed configuration and the stowed configuration is accompanied by coiling of the longerons about the longitudinal axis of the mast so that the mast structure assumes a coiled position.
These known structures have proven to be satisfactory and have been employed as booms destined to support large solar arrays of a communications satellite as well as instruments and antennae on scientific spacecrafts. The spectic strength, i.e., strength-to-weight ratio, of the known structure, disclosed in U.S. Pat. No. 3,486,279, has been increased substantially, as disclosed in U.S. Pat. No. 4,334,391, by doubling the number of lateral elements. The diagonal members of this latter construction are connected to the longerons such that adjacent bays overlap substantially. In addition to the increased specific strength, the reliability of this construction is improved because the structural integrity is maintained even when one of the lateral elements is destroyed.
Nevertheless, applications which are envisioned for the future, such as proposed space stations, require structures having long useful lives in more hostile environments where the structures are exposed to space debris, or for flights which pass through asteroid belts or planetary rings. For such applications, there is reason to believe that the structures described above could not be relied upon to provide the requisite reliability, particularly since structural damage to any one longeron would be expected to destroy the structural integrity of the mast and would cause it to collapse to a greater or lesser extent.